Types Of Roots

When a seed sprouts, it produces a primary root. If this first root becomes the largest root, it is called a taproot, as illustrated in Figure 29-3a. Many plants, like carrots and certain trees, have taproots. Contrary to what you might think, even taproots rarely penetrate the ground more than a meter or two. A few species, such as cottonwoods, do have some roots that grow 50 m (164 ft) deep to tap into underground water supplies.

In some plants, the primary root does not become large. Instead, numerous small roots develop and branch to produce a fibrous root system, like that shown in Figure 29-3b. Many mono-cots, such as grasses, have fibrous root systems. Fibrous roots of monocots often develop from the base of the stem rather than from other roots.

objectives

• Explain the difference between a taproot, a fibrous root system, and an adventitious root.

Plants can have either a taproot or a fibrous root system. (a) Many dicots, including the radish, have a large central taproot with small lateral roots. (b) Most monocots, including grasses, have a highly branched fibrous root system.

Plants can have either a taproot or a fibrous root system. (a) Many dicots, including the radish, have a large central taproot with small lateral roots. (b) Most monocots, including grasses, have a highly branched fibrous root system.

figure 29-4

Some plants grow adventitious roots from above-ground parts, including stems and leaves. (a) Corn plants grow prop roots at their base to provide additional stability. (b) This orchid grows aerial roots, which absorb water and mineral nutrients from the surface of the tree and from the air.

figure 29-5

The root tip of this seedling has many root hairs, which increase surface area and help the plant absorb water and mineral nutrients from the soil. The root cap protects the apical meristem of a root tip.

figure 29-5

The root tip of this seedling has many root hairs, which increase surface area and help the plant absorb water and mineral nutrients from the soil. The root cap protects the apical meristem of a root tip.

figure 29-4

Some plants grow adventitious roots from above-ground parts, including stems and leaves. (a) Corn plants grow prop roots at their base to provide additional stability. (b) This orchid grows aerial roots, which absorb water and mineral nutrients from the surface of the tree and from the air.

Specialized roots that grow from uncommon places, such as stems and leaves, are called adventitious roots. Figure 29-4a shows the prop roots of corn, which help keep the plant's stems upright. The aerial roots of an epiphytic orchid, shown in Figure 29-4b, obtain water and mineral nutrients from the air. Aerial roots on the stems of ivy and other vines enable them to climb walls and trees.